During development and throughout adult life certain populations of neurons are proliferating, migrating to their sites of action, and extending axons towards appropriate targets. These processes are regulated by many post-translational modifications, including proteolysis. Defects in these processes have been found to result in neurological disorders such as schizophrenia and Kallmann syndrome. A protease, carboxypeptidase A6 (CPA6), involved in cleavage of C-terminal hydrophobic amino acids, has been implicated in the mechanisms of cranial nerve development and axon guidance towards its target muscle. Specifically, a patient with a mutation disrupting CPA6 has been diagnosed with Duane syndrome, a defect in the innervation of the lateral rectus eye muscle by the abducens nerve. CPA6 is expressed in the lateral rectus eye muscle during development as well as in the adult olfactory bulb. This restricted expression in the adult olfactory bulb further implicates CPA6 in neuronal migration, as the olfactory bulb is one of the few locations of adult neuronal migration. The goal of this project is to investigate the role of CPA6 in regulating neuronal migration and axon guidance in the developing brain. First, the enzymatic properties of purified CPA6 will be assessed and substrates of CPA6 will be identified through established peptidomics techniques. The distribution of CPA6 will be characterized in detail throughout the development of the zebrafish using in situ hybridization, while the distribution of CPA6 in the mouse will be pursued by a collaborator. Finally, the genetically and microscopically tractable zebrafish system will be employed to assess the in vivo role of CPA6. Specific inhibitors as well as morpholino-mediated knockdown and plasmid- based overexpression of CPA6, followed by microscopic and physiological analysis, will be used to assess the role of CPA6 in neuronal migration and axonal guidance in vivo. This research will increase our understanding of post-translational regulation of neuronal guidance mechanisms during development. It will also shed light on the molecular defects leading to Duane syndrome, a syndrome affecting as much as 0.1% of the population.